The personal computer keyboard commonly used in the English-speaking area, is consisting of five rows of character keys, and at the center of the bottom row, there is a large space key which have several times width of a general character key. Shift keys and control keys are placed on the outer edges of the character key column, and designed to be co-operated with the little finger of the opposite side to the hand which stretch the character key (FIG. 5). Such key arrangement is taken over from the design of the mechanical typewriter which was dominant in the 19th century.
Also in the JIS (Japanese Industrial Standards) keyboard for input Japanese, the space key is placed in the bottom center of the character key column, typically have 2 or more times width of a general character key. The placement of shift keys and control keys of the JIS keyboard is in compliance with that of the keyboard for English (FIG. 6).
In contrast, in the Utility Model 61-42176 and JP-B-63-49262, as the keyboard for the Japanese word processor, so-called “thumb shift keyboard” was proposed. In the thumb shift keyboard, the thumb shift keys are placed in the position where 2 thumbs are passively placed when other fingers touch their home position of the general key operation of keyboards. Hereinafter, these 2 position of thumbs are referred as the home positions of the thumbs. In the thumb shift keyboard, an operator can input three characters with the single character key by co-push with the 2 thumb shift keys.
In the common English keyboard, which has the key arrangement called “QWERTY layout”, the home position of each finger is as follows: the left little finger is on A key, the left ring finger is on S key, the left middle finger is on D key, the left index finger is on F key. And the right index finger is on J key, the right middle finger is on K key, the right ring finger is on L key, the right little finger is on; key. When a Japanese man of average size hands places his each finger on the home position, his left thumb will generally be located in front of V key, and his right thumb will generally be located in front of N key. Therefore, if expressed with the QWERTY layout, the home position of the thumbs in the present invention is defined as follows: the home position of the left thumb is the area in contact with the lower end of V key, and that of the right thumb is the area in contact with the lower end of N key.
In the thumb shift keyboard, the key which placed on the home position of each thumb, has more than double width of that of character key. Adding that, in the thumb shift keyboard, there are two shift keys and two control keys, apart from the two thumb shift keys for Japanese. These keys are arranged on the outer edge of the character key columns, similarly to the arrangement in the English keyboard (FIG. 7).
Since the 1990's, the mainstream of Japanese input device has transferred to the personal computer from the word processor, and several keyboard arrangements for the personal computer were devised, which have the feature of the thumb shift keyboard, prepare the independence keys to the home position of each thumb. In U.S. Pat. No. 4,894,032, “the keyboard, based on the commonly used JIS Kana array keyboard, the space key split in the middle, the half of that is for enter/return key” was devised. Also in U.S. Pat. No. 5,209,812, “the keyboard which has the split space key, the half of that is for henkan function and the other half is for muhenkane function” was devised.
However, both of these two invention have the neither idea, “by limiting the width of the key placed on the home position of the thumb, making it possible to place the another key in the middle of them, and making it easy to operate with touch typing these three keys and two keys at the right and left side of them”, nor “by changing the arrangement of shift keys and control keys, making it easy to co-operate with other keys”.